Preparation of biodegradable, biocompatible microparticles containing a biologically active agent

ABSTRACT

A method for preparing biodegradable, biocompatible microparticles. A first phase is prepared that includes a biodegradable, biocompatible polymer, an active agent, and a solvent. An immiscible second phase is prepared. The first and second phases are combined to form an emulsion in which the first phase is discontinuous and the second phase is continuous. The two phases are immersed in a quench liquid that includes a quench medium and a quantity of the solvent. The quantity of the solvent is selected to control a rate of extraction of the solvent from the first phase. The first phase is isolated in the form of microparticles. Also disclosed is a microencapsulated active agent prepared by the method for preparing biodegradable, biocompatible microparticles.

This application is a continuation of application Ser. No. 08/850,679,filed May 2, 1997, which claims priority to provisional application Ser.No. 60/041,551, filed May 7, 1996, the entirety of which is herebyincorporated by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to microparticles having a reduced level ofresidual solvent(s) and to a method for the preparation of suchmicroparticles. More particularly, the present invention relates topharmaceutical compositions comprising controlled-release microparticleshaving improved shelf-life, said microparticles comprising active agentsencapsulated within a polymeric matrix, and to a method for forming suchmicroparticles.

2. Description of the Related Art

Compounds can be encapsulated in the form of microparticles by a varietyof known methods. It is particularly advantageous to encapsulate abiologically active or pharmaceutically active agent within abiocompatible, biodegradable, wall-forming material (e.g., a polymer) toprovide sustained or delayed release of drugs or other active agents. Inthese methods, the material to be encapsulated (drugs or other activeagents) is generally dissolved, dispersed, or emulsified, using knownmixing techniques, in a solvent containing the wall-forming material.Solvent is then removed from the microparticles and thereafter themicroparticle product is obtained.

An example of a conventional microencapsulation process is disclosed inU.S. Pat. No. 3,737,337 wherein a solution of a wall or shell formingpolymeric material in a solvent is prepared. The solvent is onlypartially miscible in water. A solid or core material is dissolved ordispersed in the polymer-containing solution and, thereafter, thecore-material-containing solution is dispersed in an aqueous liquid thatis immiscible in the organic solvent in order to remove solvent from themicroparticles.

Another example of a process in which solvent is removed frommicroparticles containing a substance is disclosed in U.S. Pat. No.3,523,906. In this process, a material to be encapsulated is emulsifiedin a solution of a polymeric material in a solvent that is immiscible inwater and then the emulsion is emulsified in an aqueous solutioncontaining a hydrophilic colloid. Solvent removal from themicroparticles is then accomplished by evaporation and the product isobtained.

In still another process, as disclosed in U.S. Pat. No. 3,691,090,organic solvent is evaporated from a dispersion of microparticles in anaqueous medium, preferably under reduced pressure.

Similarly, U.S. Pat. No. 3,891,570 discloses a method in whichmicroparticles are prepared by dissolving or dispersing a core materialin a solution of a wall material dissolved in a solvent having adielectric constant of 10 or less and poor miscibility with a polyhydricalcohol, then emulsifying in fine droplets through dispersion orsolution into the polyhydric alcohol and finally evaporating the solventby the application of heat or by subjecting the microparticles toreduced pressure.

Another example of a process in which an active agent may beencapsulated is disclosed in U.S. Pat. No. 3,960,757. Encapsulatedmedicaments are prepared by dissolving a wall material for capsules inat least one organic solvent, poorly miscible with water, that has aboiling point of less than 100° C., a vapor pressure higher than that ofwater, and a dielectric constant of less than about 10; dissolving ordispersing a medicament that is insoluble or slightly soluble in waterin the resulting solution; dispersing the resulting solution ordispersion to the form of fine drops in a liquid vehicle comprising anaqueous solution of a hydrophilic colloid or a surface active agent, andthen removing the organic solvent by evaporation.

Tice et al. in U.S. Pat. No. 4,389,330 describe the preparation ofmicroparticles containing an active agent by using a two-step solventremoval process. In the Tice et al. process, the active agent and thepolymer are dissolved in a solvent. The mixture of ingredients in thesolvent is then emulsified in a continuous-phase processing medium thatis immiscible with the solvent. A dispersion of microparticlescontaining the indicated ingredients is formed in the continuous-phasemedium by mechanical agitation of the mixed materials. From thisdispersion, the organic solvent can be partially removed in the firststep of the solvent removal process. After the first stage, thedispersed microparticles are isolated from the continuous-phaseprocessing medium by any convenient means of separation. Following theisolation, the remainder of the solvent in the microparticles is removedby extraction. After the remainder of the solvent has been removed fromthe microparticles, they are dried by exposure to air or by otherconventional drying techniques.

Tice et al., in U.S. Pat. No. 4,530,840, describe the preparation ofmicroparticles containing an anti-inflammatory active agent by a methodcomprising: (a) dissolving or dispersing an anti-inflammatory agent in asolvent and dissolving a biocompatible and biodegradable wall formingmaterial in that solvent; (b) dispersing the solvent containing theanti-inflammatory agent and wall forming material in a continuous-phaseprocessing medium; (c) evaporating a portion of the solvent from thedispersion of step (b), thereby forming microparticles containing theanti-inflammatory agent in the suspension; and (d) extracting theremainder of the solvent from the microparticles.

WO 90/13361 discloses a method of microencapsulating an agent to form amicroencapsulated product, having the steps of dispersing an effectiveamount of the agent in a solvent containing a dissolved wall formingmaterial to form a dispersion; combining the dispersion with aneffective amount of a continuous process medium to form an emulsion thatcontains the process medium and microdroplets having the agent, thesolvent, and the wall forming material; and adding the emulsion rapidlyto an effective amount of an extraction medium to extract the solventfrom the mnicrodroplets to form the microencapsulated product.

Bodmeier, R., et al., International Journal of Pharmaceutics 43: 179-186(1988), disclose the preparation of microparticles containing quinidineor quinidine sulfate as the active agent and poly(D,L-lactide) as thebinder using a variety of solvents including methylene chloride,chloroform, and benzene as well as mixtures of methylene chloride and awater miscible liquid, such as acetone, ethyl acetate, methanol,dimethylsulfoxide, chloroform, or benzene to enhance drug content.

Beck, L. R., et al., Biology of Reproduction 28: 186-195 (1983),disclose a process for encapsulating norethisterone in a copolymer ofD,L-lactide and glycolide by dissolving both the copolymer and thenorethisterone in a mixture of chloroform and acetone that is added to astirred cold aqueous solution of polyvinyl alcohol to form an emulsionand the volatile solvents removed under reduced pressure to yieldmicrocapsules.

Kino et al., in WO 94/10982, disclose sustained-release microspheresconsisting of a hydrophobic antipsychotic agent encapsulated in abiodegradable, biocompatible high polymer. The antipsychotic may befluphenazine, chlorpromazine, sulpiride, carpipramine, clocapramine,mosapramine, risperidone, clozapine, olanzapine, sertindole, or (pref.)haloperidol or bromperidol. The biodegradable, biocompatible highpolymer may be a fatty acid ester (co)polymer, polyacrylic acid ester,polyhydroxylactic acid, polyalkylene oxalate, polyorthoester,polycarbonate or polyamino acid. The polymer or copolymer of a fattyacid ester can be polylactic acid, polyglycolic acid, polycitric acid,polymalic acid, or lactic/glycolic acid copolymer. Also disclosed asbeing useful are poly(α-cyanoacrylic acid ester), poly(β-hydroxylacticacid), poly(tetramethylene oxalate), poly(ethylene carbonate),poly-γ-benzyl-L-glutamic acid, and poly-L-alanine.

The antipsychotic (pref. with mean particle diameter below 5 microns) issuspended in the biodegradable high polymer dissolved in an oil solvent(boiling at 120° C. or below), added to water containing an emulsifier(such as an anionic or nonionic surfactant, PVP, polyvinyl alcohol, CMC,lecithin or gelatine), emulsified and dried.

The uses and advantages are said to be: administration of theantipsychotic can be carried out by injection (e.g., subcutaneous orintramuscular) at extended intervals (e.g., every one to eight weeks);compliance during antipsychotic maintenance therapy is improved; theneed for surgical implantation is avoided; and administration is carriedout with negligible discomfort.

Very often the solvents used in the known microencapsulation processesare halogenated hydrocarbons, particularly chloroform or methylenechloride, which act as solvents for both the active agent and theencapsulating polymer. The presence of small, but detectable,halogenated hydrocarbon residuals in the final product, however, isundesirable, because of their general toxicity and possible carcinogenicactivity.

In Ramstack et al., U.S. application Ser. No. 08/298,787, now U.S. Pat.No. 5,650,173 the entirety of which is incorporated herein by reference,a process was disclosed for preparing biodegradable, biocompatiblemicroparticles comprising a biodegradable, biocompatible polymericbinder and a biologically active agent, wherein a blend of at least twosubstantially non-toxic solvents, free of halogenated hydrocarbons, wasused to dissolve both the agent and the polymer. The solvent blendcontaining the dissolved agent and polymer was dispersed in an aqueoussolution to form droplets. The resulting emulsion was then added to anaqueous extraction medium preferably containing at least one of thesolvents of the blend, whereby the rate of extraction of each solventwas controlled, whereupon the biodegradable, biocompatiblemicroparticles containing the biologically active agent were formed. Thepreferred active agents for encapsulation by this process werenorethindrone, risperidone, and testosterone and the preferred solventblend was one comprising benzyl alcohol and ethyl acetate.

Risperidone encapsulated in microparticles prepared using a benzylalcohol and ethyl acetate solvent system is also described in Mesens etal., U.S. patent application Ser. No. 08/403,432, now U.S. Pat. No.5,688,801 the entirety of which is also incorporated herein byreference.

In the course of the continuing development of the aforementionedmicroencapsulated risperidone product with the ultimate goal ofcommercialization, it was discovered that the maintenance of the productintegrity upon long-term storage was a problem, i.e., a degradationprocess was taking place. A need therefore was found to exist for ameans by which the degradation rate could be reduced, thereby increasingthe shelf-life of the product and enhancing its commercial feasibility.

SUMMARY OF THE INVENTION

The present inventors discovered that, by reducing the level of residualprocessing solvent, the rate of degradation of the product could besignificantly diminished. The present inventors discovered that onedegradation process resulted, at least in part, from hydrolysis of thepolymeric matrix, and that the rate of hydrolysis was directlyinfluenced by the level of residual processing solvent, i.e., benzylalcohol, in the product. By reducing the level of residual solvent inthe microparticles, the rate of degradation was reduced, therebyincreasing shelf-life.

The present invention relates to an improved method of preparing apharmaceutical composition in microparticle form designed for thecontrolled release of an effective amount of a drug over an extendedperiod of time, whereby the composition exhibits increased shelf-life.The useful shelf-life can be increased to about two or more years formicroparticles made in accordance with the method of the presentinvention. The invention also relates to the novel composition, per se,which comprises at least one active agent, at least one biocompatible,biodegradable encapsulating binder, and less than about two percent byweight residual solvent, the residual solvent being residual derivedfrom a solvent employed in the preparation of the microparticles.

More particularly, the present invention relates to a method forpreparing biodegradable, biocompatible microparticles comprising:

A) preparing a first phase comprising:

(1) a biodegradable, biocompatible polymeric encapsulating binder, and

(2) an active agent having limited water solubility dissolved ordispersed in a first solvent;

B) preparing an aqueous second phase;

C) combining said first phase and said second phase under the influenceof mixing means to form an emulsion in which said first phase isdiscontinuous and said second phase is continuous;

D) separating said discontinuous first phase from said continuous secondphase; and

E) washing said discontinuous first phase with

(1) water at a temperature in the range of from about 25° C. to about40° C., or

(2) an aqueous solution comprising water and a second solvent forresidual first solvent in said first phase,

thereby reducing the level of residual first solvent to less than about2% by weight of said microparticles.

In a preferred aspect of the above-described process, a quench step isadditionally performed between steps C) and D).

The aqueous second phase can be an aqueous solution of a hydrophiliccolloid or a surfactant. The aqueous second phase can be water.

In another aspect, the present invention relates to a method forpreparing biodegradable, biocompatible microparticles comprising:preparing a first discontinuous phase (also referred to herein as an"oil phase" or an "organic phase") containing from about 5 weightpercent to about 50 weight percent solids of which from about 5 to about95 weight percent is a solution of biodegradable, biocompatiblepolymeric encapsulating binder and incorporating from about 5 to about95 weight percent, as based on polymeric binder, of an active agent in asolvent blend, the blend comprising first and second mutually miscibleco-solvents, each having a solubility in water of from about 0.1 toabout 25 weight percent at 20° C.; forming an emulsion containing from1:1 to 1:10 of the first phase in an emulsion process medium to formmicrodroplets of the discontinuous first phase composition in acontinuous or "aqueous" second phase processing medium; adding thecombined first and second phases to an aqueous extraction quench liquidat a level of from about 0.1 to about 20 liters of aqueous quench liquidper gram of polymer and active agent, the quench liquid containing themore water soluble co-solvent of the blend at a level of from about 20%to about 70% of the saturation level of the more water solubleco-solvent in the quench liquid at the temperature being used;recovering microparticles from the quench liquid; and washing thediscontinuous first phase with water at an elevated temperature (i.e.,above room temperature) or with an aqueous solution comprising water anda solvent for residual solvent in the first phase, thereby reducing thelevel of residual solvent in the microparticles. The level of residualsolvent in the microparticles is preferably reduced to about 2% byweight of the microparticles.

In another aspect, the present invention relates to a method forpreparing biodegradable, biocompatible microparticles comprising:

A) preparing a first phase comprising

1) a biodegradable, biocompatible polymeric encapsulating binderselected from the group consisting of poly(glycolic acid),poly-d,l-lactic acid, poly-l-lactic acid, and copolymers of theforegoing, and

2) an active agent selected from the group consisting of risperidone and9-hydroxy risperidone, dissolved or dispersed in a blend comprisingethyl acetate and benzyl alcohol, said blend being free from halogenatedhydrocarbons;

B) preparing a second phase comprising polyvinyl alcohol dissolved inwater;

C) combining said first phase and said second phase in a static mixer toform an emulsion in which said first phase is discontinuous and saidsecond phase is continuous;

D) immersing said first and said second phases in a quench liquid;

E) isolating said discontinuous first phase in the form ofmicroparticles; and

F) washing said discontinuous first phase with an aqueous solutioncomprising water and ethanol, thereby reducing the level of benzylalcohol to less than about 2% by weight of said microparticles.

In another aspect, the invention is directed to a method of preparingbiodegradable, bicompatible microparticles comprising: preparing a firstphase, said first phase comprising a biologically active agent, abiodegradable, biocompatible polymer, and a first solvent; preparing asecond phase, wherein said first phase is substantially immiscible insaid second phase; flowing said first phase through a static mixer at afirst flow rate; flowing said second phase through said static mixer ata second flow rate so that said first phase and said second phase flowsimultaneously through said static mixer thereby forming microparticlescontaining said active agent; isolating said microparticles; and washingsaid microparticles with water at an elevated temperature or with anaqueous solution comprising water and a second solvent for residualfirst solvent in said microparticles, thereby reducing the level ofresidual first solvent to less than about 2% by weight of saidmicroparticles.

In further aspects of the invention, the first phase is prepared by:dissolving the biologically active agent in a solution of the polymerdissolved in a solvent free from halogenated hydrocarbons; preparing adispersion comprising the active agent in the polymer solution; orpreparing an emulsion comprising the active agent in the polymersolution.

In another aspect, the present invention relates to a pharmaceuticalcomposition comprising biodegradable and biocompatible microparticles ina pharmaceutically acceptable carrier. The microparticles comprise apolymeric encapsulating binder having dispersed or dissolved therein anactive agent, and less than about 2% by weight residual solvent, whereinthe residual solvent is residual derived from a solvent employed in thepreparation of the microparticles.

In another aspect, the present invention relates to a pharmaceuticalcomposition comprising biodegradable and biocompatible microparticles,ranging in size from about 25 to about 180 microns, in apharmaceutically acceptable carrier. The microparticles comprise acopolymer of poly(glycolic acid) and poly(d,l-lactic acid) wherein themolar ratio of lactide to glycolide is in the range of from about 85:15to about 50:50 and having dispersed or dissolved therein from about 35to about 40% of an active agent comprising risperidone or9-hydroxy-risperidone, and from about 0.5 to about 1.5% by weight ofbenzyl alcohol.

In yet another aspect, the invention provides a method for preparingbiodegradable, biocompatible microparticles that comprises contactingmicroparticles comprising a biodegradable, biocompatible polymer matrixcontaining an active agent and an organic solvent with an aqueouswashing system to thereby reduce the level of residual organic solventto less than about 2% by weight of the microparticles. The aqueouswashing system is: (1) at a temperature of from about 25° C. to about40° C. for at least part of the contacting step; or (2) an aqueoussolution comprising water and a water-miscible solvent for the organicsolvent. The microparticles are recovered from the aqueous washingsystem.

In the process of the invention, the initial content of organic solventin the microparticles will generally be above 3.5%, more generally above4.0% of the total weight of the microparticles. Advantageously, theprocess will reduce this content to less than 2%, preferably to lessthan 1.5% and most preferably to less than 1%. The organic solventpreferably contains a hydrophobic group containing at least 5 carbons,e.g., an aryl group such as a naphthyl or more especially a phenylgroup.

The organic solvent in the microparticles will generally be present as aresult of a particle formation process where the microparticles havebeen produced from a solution of the matrix forming polymer material inthe organic solvent or in a solvent mixture or blend containing theorganic solvent.

The organic solvent will preferably be a non-halogenated solvent. Morepreferably, the organic solvent will be an at least partiallywater-miscible solvent, such as an alcohol (e.g., benzyl alcohol), alinear or cyclic ether, a ketone or an ester (e.g., ethyl acetate).

Where used, a co-solvent in the solvent mixture or blend likewise willpreferably be a non-halogenated solvent and particularly preferably willbe an at least partially water-miscible solvent such as an alcohol(e.g., a C₁₋₄ alkanol such as ethanol), a linear or cyclic ether, aketone or an ester.

The contacting with the aqueous washing system may be effected in one ormore stages, e.g., a single contact or a series of washes, optionallywith differently constituted aqueous washing systems. Preferably, thetotal contact time is for a period of ten minutes to several hours,e.g., 1 to 48 hours.

The matrix forming polymer material should of course have sufficientlylimited solubility in the aqueous washing system used that the particlesdo not dissolve completely in the washing system during the contactperiod.

The process of the present invention may be carried out using pre-formedmicroparticles or, more preferably, may additionally comprise theproduction of the microparticles, conveniently using a liquid phasecontaining as a solvent or co-solvent the organic solvent referred toabove, as well as the matrix forming polymer and the active agent.Particle formation may then be effected, for example, by spray dryingor, more preferably, by forming an emulsion using a second liquid phase,e.g., an aqueous phase, with the first liquid phase being discontinuousand the second being continuous as described above.

Viewed from a further aspect, the invention provides the use ofmicroparticles prepared by the process of the invention for themanufacture of a medicament for use in a method of diagnosis or therapy.

Viewed from a yet still further aspect, the invention provides a methodof treatment of the human or non-human (e.g., mammalian) animal bodycomprising the administration thereto of a composition according to theinvention.

ADVANTAGES OF THE INVENTION

Advantages of the method of the present invention are that it provides,inter alia, a biodegradable, biocompatible system that can be injectedinto a patient, the ability to mix microparticles containing differentdrugs, microparticles free from halogenated hydrocarbon residues, theability to program release (multiphasic release patterns) to give fasteror slower rates of drug release as needed, and improved shelf-lifestability resulting from lowered residual solvent in the finishedproduct.

An advantage of the products prepared by the method of the presentinvention is that durations of action ranging from 14 to more than 200days can be obtained, depending upon the type of microparticle selected.In preferred embodiments, the microparticles are designed to affordtreatment to patients during duration of action periods of 30 to 60 daysand 60 to 100 days. A 90 day duration of action period is considered tobe particularly advantageous. The duration of action can be controlledby manipulation of the polymer composition, polymer: drug ratio,microparticle size, and concentration of residual solvent remaining inthe microparticle after treatment.

Another important advantage of the microparticles prepared by theprocess of the present invention is that practically all of the activeagent is delivered to the patient because the polymer used in the methodof the present invention is biodegradable, thereby permitting all of theentrapped active agent to be released into the patient.

Still another important advantage of the microparticles prepared by theprocess of the present invention is that residual solvent(s) in thefinished microparticle can be reduced by approximately an order ofmagnitude whereby the usefull shelf-life of the product can be increasedfrom about six months for product made without the washing step of thepresent invention to about two or more years for particles made with thewashing step.

A further advantage of the process of the present invention is that itmay prove beneficial in controlling the release characteristics ofactive agent in vivo or reducing an undesirable or possibly harmfulsolvent.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 depicts a graph showing the reduction in benzyl alcohol levels inthe finished product as a function of ethanol concentration (5%; 15%;20%; 25%) in an ethanol: water wash;

FIG. 2 depicts a graph showing the impact of microparticle concentrationon the level of residual benzyl alcohol (BA) in the finished product;

FIG. 3 depicts a graph showing the impact of temperature of the washstep on the level of residual benzyl alcohol (BA) in the finishedproduct; and

FIG. 4 depicts a graph showing the effect of the level of residualsolvent (benzyl alcohol) on the decay in molecular weight of thepolymeric matrix.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

To ensure clarity of the description that follows, the followingdefinitions are provided. By "microparticles" or "microspheres" is meantsolid particles that contain an active agent dispersed or dissolvedwithin a biodegradable, biocompatible polymer that serves as the matrixof the particle. By "limited water solubility" is meant having asolubility in water in the range of from about 0.1 to about 25 wt. % at20° C. By "halogenated hydrocarbons" is meant halogenated organicsolvents, i.e., C₁ -C₄ halogenated alkanes, e.g., methylene chloride,chloroform, methyl chloride, carbon tetrachloride, ethylene dichloride,ethylene chloride, 2,2,2-trichloroethane, and the like. By"biodegradable" is meant a material that should degrade by bodilyprocesses to products readily disposable by the body and should notaccumulate in the body. The products of the biodegration should also bebiocompatible with the body. By "biocompatible" is meant not toxic tothe human body, is pharmaceutically acceptable, is not carcinogenic, anddoes not significantly induce inflammation in body tissues. By "weight%" or "% by weight" is meant parts by weight per total weight ofmicroparticle. For example, 10 wt. % agent would mean 10 parts agent byweight and 90 parts polymer by weight.

In the process of the present invention, a solvent, preferably free fromhalogenated hydrocarbons, is used to produce biodegradable,biocompatible microparticles comprising at least one biologically activeagent. A particularly preferred solvent is a solvent blend comprising atleast two solvents. A first solvent component of the solvent blend is apoor solvent for the active agent, but is a good solvent for thebiodegradable, biocompatible polymer used herein. A second solventcomponent of the solvent blend is a good solvent for the active agent.The active agent is dissolved or dispersed in the solvent. Polymermatrix material is added to the agent-containing medium in an amountrelative to the active agent that provides a product having the desiredloading of active agent. Optionally, all of the ingredients of themicroparticle product can be blended in the solvent blend mediumtogether.

The preferred solvent system is a blend of at least two solvents. Thesolvents in the solvent blend are preferably:

(1) mutually miscible with one another,

(2) capable, when blended, of dissolving or dispersing the active agent,

(3) capable, when blended, of dissolving polymeric matrix material,

(4) chemically inert to the active agent,

(5) biocompatible,

(6) substantially immiscible with any quench liquid employed, i.e.,having a solubility from about 0.1 to 25%, and

(7) solvents other than halogenated hydrocarbons.

An ideal solvent blend for encapsulation of an active agent should havea high solubility for the polymeric encapsulating agent of generally atleast about 5 weight percent and, preferably, at least about 20 weightpercent at 20° C. The upper limit of solubility is not critical, but ifover about 50 weight percent of the solution is encapsulating polymer,the solution may become too viscous to handle effectively andconveniently. This is, of course, dependent on the nature of theencapsulating polymer and its molecular weight.

The solvent system, although substantially immiscible with thecontinuous phase process medium and any quenching liquid, which usuallyare water or water-based, preferably has a limited solubility therein.If the solvent system were infinitely soluble in the process medium,microparticles would be unable to form during the emulsion phase; if thesolubility of the solvent system in an extractive quenching medium weretoo low, however, large quantities of quenching medium would be needed.Generally, solvent solubilities of from about 0.1 to about 25% in theprocess medium and any quench medium are acceptable for use herein. Itwill often be advantageous for the quench medium, if employed, tocontain from about 70 to about 20 weight percent of the saturation pointof the first solvent, i.e., the solvent of higher solubility in thequench medium, to control the rate of loss of the first solvent from themicroparticles into the quench medium.

Added considerations in choosing a component of the solvent blend of thepresent invention include boiling point (i.e., the ease with which thesolvents can be evaporated, if desired, to form finished product) andspecific gravity (tendency of the discontinuous or oil phase to floatduring emulsifying and quenching). Finally, the solvent system shouldhave low toxicity.

Generally, the solvent blend composition of two components will containfrom about 25 to about 75 weight percent of the first solvent, and,correspondingly, from about 75 to about 25 weight percent of the secondsolvent.

Experiments using benzyl alcohol alone as the solvent did result incontrol of microparticle size as determined by inspection of the quenchtank contents by optical microscopy. Upon drying, however, generallypoor quality was found to have resulted. Often, recovery was difficultbecause of stickiness. Also, solvent residuals tended to be elevated.Using a solvent system of ethyl acetate and benzyl alcohol for thediscontinuous or oil phase improved the microparticle quality andrelease characteristics.

The solvent blend of the present invention is preferably a blend of atleast two of the following: an ester, an alcohol, and a ketone.Preferred esters are of the structure R¹ COOR² where R¹ and R² areindependently selected from the group consisting of alkyl moieties offrom 1 to 4 carbon atoms, i.e., methyl, ethyl, propyl, butyl, andisomers thereof. The most preferred ester for use as one component ofthe solvent blend employed in the practice of the present invention isethyl acetate.

Preferred alcohols are of the structure R³ CH₂ OH where R³ is selectedfrom the group consisting of hydrogen, alkyl of from 1 to 3 carbonatoms, and aryl of from 6 to 10 carbon atoms. It is more preferred thatR³ be aryl. The most preferred alcohol for use as one component of thesolvent blend employed in the practice of the present invention isbenzyl alcohol.

Preferred ketones are of the structure R⁴ COR⁵ where R⁴ is selected fromthe group consisting of alkyl moieties of from 1 to 4 carbon atoms,i.e., methyl, ethyl, propyl, butyl, and isomers thereof and R⁵ isselected from the group consisting of alkyl moieties of from 2 to 4carbon atoms, i.e., ethyl, propyl, butyl, and isomers thereof. The mostpreferred ketone for use as one component of the solvent blend employedin the practice of the present invention is methyl ethyl ketone.

The polymer matrix material of the microparticles prepared by theprocess of the present invention is biocompatible and biodegradable. Thematrix material should be biodegradable in the sense that it shoulddegrade by bodily processes to products readily disposable by the bodyand should not accumulate in the body. The products of thebiodegradation should also be biocompatible with the body, as should anyresidual solvent that may remain in the microparticles.

Preferred examples of polymer matrix materials include poly(glycolicacid), poly(d,l-lactic acid), poly(l-lactic acid), copolymers of theforegoing, and the like. Various commercially available poly(lactide-co-glycolide) materials (PLGA) may be used in the method of thepresent invention. For example, poly (d,1-lactic-co-glycolic acid) iscommercially available from Medisorb Technologies International L. P.(Cincinnati, Ohio). A suitable product commercially available fromMedisorb is a 50:50 poly (d,l lactic co-glycolic acid) known asMEDISORB® 50:50 DL. This product has a mole percent composition of 50%lactide and 50% glycolide. Other suitable commercially availableproducts are MEDISORB® 65:35 DL, 75:25 DL, 85:15 DL and poly(d,l-lacticacid) (d,1-PLA). Poly(lactide-co-glycolides) are also commerciallyavailable from Boehringer Ingelheim (Germany) under its Resomer mark,e.g., PLGA 50:50 (Resomer RG 502), PLGA 75:25 (Resomer RG 752) andd,l-PLA (Resomer RG 206), and from Birmingham Polymers (Birmingham,Ala.). These copolymers are available in a wide range of molecularweights and ratios of lactic acid to glycolic acid.

The most preferred polymer for use in the practice of this invention isthe copolymer, poly(d,l-lactide-co-glycolide). It is preferred that themolar ratio of lactide to glycolide in such a copolymer be in the rangeof from about 85:15 to about 50:50.

It will be understood that the problem addressed by the process of thepresent invention is the undesirably short shelf-life engendered by theaction of an active agent on the matrix polymer where the solvent, or atleast one of the solvents of the solvent blend, used in making themicroparticles remains in sufficient concentration in the finishedproduct to exacerbate degrading interaction between the active agent andthe polymer. This problem can be seen, for example, with an active agenthaving a basic moiety, such as risperidone, and a matrix polymer thathas a group or linkage susceptible to base-catalyzed hydrolysis. Thoseskilled in the art will readily comprehend, however, that the concept ofthe present invention is broader than the shelf-life problem described,and is, rather, directed to the more general solution of washingproducts having particular tenacious solvent residuals with a washliquid comprising water and a water miscible solvent for the tenacioussolvent(s) in the product.

The molecular weight of the polymeric matrix material is of someimportance. The molecular weight should be high enough to permit theformation of satisfactory polymer coatings, i.e., the polymer should bea good film former. Usually, a satisfactory molecular weight is in therange of 5,000 to 500,000 daltons, preferably about 150,000 daltons.However, since the properties of the film are also partially dependenton the particular polymeric matrix material being used, it is verydifficult to specify an appropriate molecular weight range for allpolymers. The molecular weight of a polymer is also important from thepoint of view of its influence upon the biodegradation rate of thepolymer. For a diffusional mechanism of drug release, the polymer shouldremain intact until all of the drug is released from the microparticlesand then degrade. The drug can also be released from the microparticlesas the polymeric excipient bioerodes. By an appropriate selection ofpolymeric materials a microparticle formulation can be made in which theresulting microparticles exhibit both diffusional release andbiodegradation release properties. This is useful in affordingmultiphasic release patterns.

Those skilled in the art will comprehend that removal of residualsolvent by the wash step of the present invention may have an effectupon the drug release rate, which may be either detrimental orbeneficial, depending upon the circumstances. For example, where theresidual solvent is acting as a plasticizer for the matrix polymer, theglass transition temperature may be seen to decrease, thereby possiblyaccelerating the release rate of the active agent. If, in a givensituation, a faster release rate is desirable, this result will bebeneficial. If, however, the rate becomes fast enough to negativelyaffect the desired action of the active agent with regard to thepatient, it will be incumbent upon the formulator to employ means foralleviating the accelerated release rate. Such modifications of theprocess, when required, are within the capability of those of ordinaryskill in the relevant arts and can be realized without undueexperimentation.

The formulation prepared by the process of the present inventioncontains an active agent dispersed in the microparticle polymetricmatrix material. The amount of such agent incorporated in themicroparticles usually ranges from about 1 wt. % to about 90 wt. %,preferably 30 to 50 wt. %, more preferably 35 to 40 wt.%.

In carrying out the process of the present invention, the encapsulatingpolymer should be essentially 100% dissolved in the solvent or solventblend at the time the solution is emulsified. The active agent can bedispersed or dissolved in the solvent or solvent blend at the time it isadded to the continuous phase process medium. The content of normallysolid material (active agent plus encapsulating polymer) in the solventblend at the time it is first emulsified should be at least 5 weightpercent and preferably at least 20 weight percent. Minimizing solvent inthe discontinuous or oil phase provides a better quality microparticleand requires less extraction medium.

Preferred active agents that can be encapsulated by the process of thepresent invention are those that comprise at least one basic moiety.Particularly preferred active agents that can be encapsulated by theprocess of the present invention are 1,2-benzazoles; more particularly,3-piperidinyl-substituted 1,2-benzisoxazoles and 1,2benzisothiazoles.The most preferred active agents of this kind for treatment by theprocess of the present invention are 3- 2-4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-piperidinyl!ethyl!-6,7,8,9-tetrahydro-2-methyl-4H-pyrido1,2-a!pyrimidin4-one ("risperidone") and 3- 2-4-(6-fluoro-1,2-benzisoxazol-3-yl)-1-piperidinyl!ethyl!-6,7,8,9-tetrahydro-9-hydroxy-2-methyl-4H--pyrido1,2-a!pyrimidin4-one ("9-hydroxyrisperidone") and the pharmaceuticallyacceptable salts thereof. Risperidone (which term, as used herein, isintended to include its pharmaceutically acceptable salts) is mostpreferred.

Other biologically active agents that can be incorporated using theprocess of the present invention include gastrointestinal therapeuticagents such as aluminum hydroxide, calcium carbonate, magnesiumcarbonate, sodium carbonate and the like; non-steroidal antifertilityagents; parasympathomimetic agents; psychotherapeutic agents; majortranquilizers such as chlorpromazine HCl, clozapine, mesoridazine,metiapine, reserpine, thioridazine and the like; minor tranquilizerssuch as chlordiazepoxide, diazepam, meprobamate, temazepam and the like;rhinological decongestants; sedative-hypnotics such as codeine,phenobarbital, sodium pentobarbital, sodium secobarbital and the like;steroids such as testosterone and testosterone propionate; sulfonamides;sympathomimetic agents; vaccines; vitamins and nutrients such as theessential amino acids; essential fats and the like; antimalarials suchas 4-aminoquinolines, 8-aminoquinolines, pyrimethamine and the like,anti-migraine agents such as mazindol, phentermine and the like;anti-Parkinson agents such as L-dopa; anti-spasmodics such as atropine,methscopolamine bromide and the like; antispasmodics and anticholinergicagents such as bile therapy, digestants, enzymes and the like;antitussives such as dextromethorphan, noscapine and the like;bronchodilators; cardiovascular agents such as anti-hypertensivecompounds, Rauwolfia alkaloids, coronary vasodilators, nitroglycerin,organic nitrates, pentaerythritotetranitrate and the like; electrolytereplacements such as potassium chloride; ergotalkaloids such asergotamine with and without caffeine, hydrogenated ergot alkaloids,dihydroergocristine methanesulfate, dihydroergocornine methanesulfonate,dihydroergokroyptine methanesulfate and combinations thereof; alkaloidssuch as atropine sulfate, Belladonna, hyoscine hydrobromide and thelike; analgetics; narcotics such as codeine, dihydrocodienone,meperidine, morphine and the like; non-narcotics such as salicylates,aspirin, acetaminnophen, d-propoxyphene and the like; antibiotics suchas the cephalosporins, chloranphenical, gentamicin, Kanamycin A,Kanamycin B, the penicillins, ampicillin, streptomycin A, antimycin A,chloropamtheniol, metromidazole, oxytetracycline penicillin G, thetetracyclines, and the like; anti-cancer agents; anti-convulsants suchas mephenytoin, phenobarbital, trimethadione; anti-emetics such asthiethylperazine; antihistamines such as chlorophinazine,dimenhydrinate, diphenhydramine, perphenazine, tripelennamine and thelike; anti-inflammatory agents such as hormonal agents, hydrocortisone,prednisolone, prednisone, non-hormonal agents, allopurinol, aspirin,indomethacin, phenylbutazone and the like; prostaglandins; cytotoxicdrugs such as thiotepa, chlorambucil, cyclophosphamide, melphalan,nitrogen mustard, methotrexate and the like; antigens of suchmicroorganisms as Neisseria gonorrhea, Mycobacterium tuberculosis,Herpes virus (humonis, types 1 and 2), Candida albicans, Candidatropicalis, Trichomonas vaginalis, Haemophilus vaginalis, Group BStreptococcus ecoli, Microplasma hominis, Hemophilus ducreyi, Granulomainguinale, Lymphopathia venereum, Treponema pallidum, Brucella abortus,Brucella melitensis, Brucella suis, Brucella canis, Campylobacter fetus,Campylobacter fetus intestinalis, Leptospira pomona, Listeriamonocytogenes, Brucella ovis, Equine herpes virus 1, Equine arteritisvirus, IBR-IBP virus, BVD-MB virus, Chlamydia psittaci, Trichomonasfoetus, Toxoplasma gondii, Escherichia coli, Actinobacillus equuli,Salmonella abortus ovis, Salmonella abortus equi, Pseudomonasaeruginosa, Corynebacterium equi, Corynebacterium pyogenes,Actinobaccilus seminis, Mycoplasma bovigenitalium, Aspergillusfumigatus, Absidia ramosa, Trypanosoma equiperdum, Babesia caballi,Clostridium tetani, and the like; antibodies that counteract the abovemicroorganisms; and enzymes such as ribonuclease, neuramidinase,trypsin, glycogen phosphorylase, sperm lactic dehydrogenase, spermhyaluronidase, adenosinetriphosphatase, alkaline phosphatase, alkalinephosphatase esterase, amino peptidase, trypsin, chymotrypsin, amylase,muramidase, acrosomal proteinase, diesterase, glutarnic aciddehydrogenase, succinic acid dehydrogenase, beta-glycophosphatase,lipase, ATP-ase alpha-peptate gamma-glutamylotranspeptidase,sterol-3-beta-ol-dehydrogenase, and DPN-di-aprorase.

Other suitable active agents include estrogens such as diethylstilbestrol, 17-beta-estradiol, estrone, ethinyl estradiol, mestranol,and the like; progestins such as norethindrone, norgestryl, ethynodioldiacetate, lynestrenol, medroxyprogesterone acetate, dimesthisterone,megestrol acetate, chlormadinone acetate, norgestimate, norethisterone,ethisterone, melengestrol, norethynodrel and the like; and spermicidalcompounds such as nonylphenoxypolyoxyethylene glycol, benzethoniumchloride, chlorindanol and the like.

Still other macromolecular bioactive agents that may be chosen forincorporation include, but are not limited to, blood clotting factors,hemopoietic factors, cytokines, interleukins, colony stimulatingfactors, growth factors, and analogs and fragments thereof.

The microparticles can be mixed by size or by type so as to provide forthe delivery of active agent to the patient in a multiphasic mannerand/or in a manner that provides different active agents to the patientat different times, or a mixture of active agents at the same time. Forexample, secondary antibiotics, vaccines, or any desired active agent,either in microparticle form or in conventional, unencapsulated form canbe blended with a primary active agent and provided to the patient.

The mixture of ingredients in the discontinuous or oil phase solventsystem is emulsified in a continuous-phase processing medium; thecontinuous-phase medium being such that a dispersion of microparticlescontaining the indicated ingredients is formed in the continuous-phasemedium.

Although not absolutely necessary, it is preferred to saturate thecontinuous phase process medium with at least one of the solventsforming the discontinuous or oil phase solvent system. This provides astable emulsion, preventing transport of solvent out of themicroparticles prior to quenching. Similarly, a vacuum may be applied asin U.S. Pat. No. 4,389,330. Where ethyl acetate and benzyl alcohol arethe components of the solvent system, the aqueous or continuous phase ofthe emulsion preferably contains 1 to 8 weight percent ethyl acetate and1 to 4 weight percent benzyl alcohol.

Usually, a surfactant or a hydrophilic colloid is added to thecontinuous-phase processing medium to prevent the solvent microdropletsfrom agglomerating and to control the size of the solvent microdropletsin the emulsion. Examples of compounds that can be used as surfactantsor hydrophilic colloids include, but are not limited to, poly(vinylalcohol), carboxymethyl cellulose, gelatin, poly(vinyl pyrrolidone),Tween 80, Tween 20, and the like. The concentration of surfactant orhydrophilic colloid in the process medium should be sufficient tostabilize the emulsion and will affect the final size of themicroparticles. Generally the concentration of the surfactant orhydrophilic colloid in the process medium will be from about 0.1% toabout 10% by weight based on the process medium, depending upon thesurfactant or hydrophilic colloid, the discontinuous or oil phasesolvent system, and the processing medium used. A preferred dispersingmedium combination is a 0.1 to 10 wt. %, more preferably 0.5 to 2 wt. %,solution of poly(vinyl alcohol) in water.

The emulsion can be formed by mechanical agitation of the mixed phasesor by adding small drops of the discontinuous phase that contains activeagent and wall forming material to the continuous phase processingmedium. The temperature during the formation of the emulsion is notespecially critical, but can influence the size and quality of themicroparticles and the solubility of the active agent in the continuousphase. Of course, it is desirable to have as little of the active agentin the continuous phase as possible. Moreover, depending upon thesolvent blend and continuous-phase processing medium employed, thetemperature must not be too low or the solvent and processing medium maysolidify or become too viscous for practical purposes. On the otherhand, it must not be so high that the processing medium will evaporateor that the liquid processing medium will not be maintained. Moreover,the temperature of the emulsion cannot be so high that the stability ofthe particular active agent being incorporated in the microparticles isadversely affected. Accordingly, the dispersion process can be conductedat any temperature that maintains stable operating conditions,preferably from about 20° C. to about 60° C., depending upon the activeagent and excipient selected.

As stated above, in order to create microparticles containing an activeagent, an organic or oil (discontinuous) phase and an aqueous phase arecombined. The organic and aqueous phases are largely or substantiallyimmiscible, with the aqueous phase constituting the continuous phase ofthe emulsion. The organic phase includes the active agent as well as thewall forming polymer, i.e., the polymeric matrix material. The organicphase is prepared by dissolving or dispersing the active agent(s) in theorganic solvent system of the present invention. The organic phase andthe aqueous phase are preferably combined under the influence of mixingmeans.

A preferred type of mixing means is a static mixer and a preferredmethod of encapsulating the active agent to form the controlled releasemicroparticles of the present invention involves the use of such astatic mixer. Preferably the combined organic and aqueous phases arepumped through a static mixer to form an emulsion and into a largevolume of quench liquid, to obtain microparticles containing the activeagent encapsulated in the polymeric matrix material. An especiallypreferred method of mixing with a static mixer in the process of thepresent invention is disclosed by Ramstack et al. in U.S. applicationSer. No. 08/338,805, (now U.S. Pat. No. 5,654,008) the entirety of whichis incorporated herein by reference.

One advantage of preparing microparticles using a static mixer is thataccurate and reliable scaling from laboratory to commercial batch sizescan be done while achieving a narrow and well defined size distributionof microparticles containing biologically or pharmaceutically activeagents. A further advantage of this method is that the same equipmentcan be used to form microparticles containing active agents of a welldefined size distribution for varying batch sizes. In addition toimproving process technology, static mixers are low maintenance, theirsmall size requires less space than dynamic mixers, and they have lowenergy demands and comparatively low investment costs.

In practice, the organic phase and the aqueous phase are mixed in astatic mixer to form an emulsion. The emulsion formed comprisesmicroparticles containing active agent encapsulated in the polymericmatrix material. Preferably, the microparticles are then stirred in atank containing a quench solution in order to remove most of the organicsolvent from the microparticles, resulting in the formation of hardenedmicroparticles.

Following the movement of the microparticles from the static mixer andentrance into the quench tank, the continuous-phase processing medium isdiluted and much of the solvent in the microparticles is removed byextraction. In this extractive quench step, the microparticles can besuspended in the same continuous-phase processing medium used duringemulsification, with or without hydrophilic colloid or surfactant, or inanother liquid. The extraction medium removes a significant portion ofthe solvent from the microparticles, but does not dissolve them. Duringthe extraction, the extraction medium containing dissolved solvent can,optionally, be removed and replaced with fresh extraction medium.

After the quench step has been completed, the microparticles can beisolated as stated above, and then may, if desired, be dried by exposureto air or by other conventional drying techniques, such as, vacuumdrying, drying over a desiccant, or the like. This process is veryefficient in encapsulating an active agent since core loadings of up toabout 80 wt. %, preferably up to about 50 wt. %, can be obtained.

When a solvent blend is used to form the organic or oil phase dropletsin the emulsion, one of the solvents in the solvent blend will beextracted in the quench step more quickly than the other solvent, e.g.,the first solvent, ethyl acetate, in the case of the preferred ethylacetate/benzyl alcohol blend. Thus, high residuals of the second solvent(here, benzyl alcohol) are left behind. Owing to the high boiling pointof benzyl alcohol, it is not easily removed by exposure of themicroparticles to air or other conventional evaporative means. Toimprove the efficiency of this procedure, some of the more rapidlyextracted solvent can be added to the quench extraction medium prior toaddition of the emulsion. The concentration of themore-rapidly-extracted solvent in the quench extraction medium generallyis from about 20 to about 70% of the saturation point of the solvent inthe medium at the temperature to be used for the extraction. Thus, whenthe emulsion is added to the quench liquid, extraction of the morerapidly extracted solvent is retarded and more of the second, moreslowly extracted, solvent is removed.

The exact amount of this more-rapidly-extracted solvent "spike" added tothe quench liquid is of importance to final microparticle quality. Toomuch solvent (i.e., near the saturation point) results in porousmicroparticles with active agent visible on the surface, causing whatmay be an undesirably high rate of release. Too little solvent in thequench medium results in high residual level of themore-slowly-extracted solvent and poor microparticle quality. Thetemperature of the quench medium is also important as it affects solventsolubility and rate of extraction.

Both temperature and amount of solvent spike can be adjusted tocontribute beneficially to the final desired product characteristics,i.e., highly porous, quick releasing microparticles, or slow releasingmicroparticles having a low porosity.

The quench liquid can be plain water, a water solution, or othersuitable liquid, the volume, amount, and type of which depends on thesolvents used in the emulsion phase. The quench liquid is preferablywater. Generally, the quench liquid volume is on the order of 10 timesthe saturated volume (i.e., 10 times the quench volume needed to absorbcompletely the volume of solvent in the emulsion). Depending on thesolvent system, however, quench volume can vary from about 2 to about 20times the saturated volume. Additionally, it is convenient to describethe quench volume requirement relative to batch size (microparticleproduct). This ratio is an indication of efficiency of the extractionstep and, in some cases, dictates the batch size for a given set ofequipment. The larger the ratio, the more volume is required per productweight. On the other hand, with a smaller ratio, more product can beobtained from the same amount of quench volume. This ratio can vary fromabout 0.1 to about 10 liters of quench volume per gram of microparticlesproduced. Processes with a ratio of less than about 1 liter per gram arepreferred.

When using the preferred solvent combination of benzyl alcohol and ethylacetate, the ethyl acetate content of the quench liquid appears toaffect the residual solvent level in the product microparticles. At lowethyl acetate contents in the quench liquid, the benzyl alcoholresiduals in the microparticles are high while ethyl acetate may bealmost non-detectable. At high ethyl acetate contents in the quenchliquid, more ethyl acetate may be retained by the microparticles thanbenzyl alcohol. At a quench volume of about 1 liter per gram of activeagent and polymeric encapsulating material being quenched, about 2-4weight percent ethyl acetate in the quench liquid is optimal at 0-10° C.

After the quenching step, the microparticles are isolated from theaqueous quench solution by any convenient means of separation--the fluidcan be decanted from the microparticles or the microparticle suspensioncan be filtered, for example, a sieve column can be used. Various othercombinations of separation techniques can be used, if desired.Filtration is preferred.

The filtered microparticles are then subjected to the washing step ofthe present invention in order to reduce still further the level ofresidual solvent(s) therein, preferably to a level in the range of fromabout 0.2 to about 2.0%. In practice, it has been found that, in thepreferred ethyl acetate/benzyl alcohol dual solvent case, residualbenzyl alcohol levels are still generally in the 4-8% range without thewashing step of the present invention. This level of residual solvent inthe microparticles appears to be sufficient to accelerate thedegradation process, thereby reducing shelf-life. Degradation of themicroparticles can occur, for example, by undesired hydrolysis of thehydrolyzable linkages of a matrix polymer by a basic active agent. Thus,the washing step(s) of the present invention are employed to reduce theresidual benzyl alcohol or other solvent content in the microparticlesto retard the degradation process.

As stated above, the wash solution comprises either water alone or,preferably, water and a solvent miscible therewith that is also a goodsolvent for the residual solvent in the microparticles. Where, as in thepreferred process of the present invention, the residual solvent isbenzyl alcohol, C₁ -C₄ aliphatic alcohols are preferred for use in thewash solution. These alcohols are methanol, ethanol, propanol, butanol,and isomers of the foregoing. The most preferred alcohol is ethanol.

The concentration of the alcohol in the wash solution can vary dependingupon the particular circumstances. Generally, the alcohol will compriseless than 50% by weight with a lower limit of about 5%. Thus, apreferred range for the alcohol concentration with normally be fromabout 5% to about 50% by weight. More preferably, the concentration willlie in the range of from about 15% to about 30%.

The temperature of the wash solution is also important to the efficiencyof the washing step. Generally, increasing the temperature will decreasethe time needed for the wash to lower the remaining residual content tothe desired level. On the other hand, too high a temperature can bedetrimental in that the softening temperature of the matrix polymer ofthe microparticles may be approached or exceeded, thereby causingclumping or stickiness. Conversely, too low a temperature may cause thematrix material to become too hard, thereby retarding the rate at whichthe residuals can be extracted, whereby the process may becomeprohibitively expensive. It has been found that a temperature range offrom about 5° C. to about 40° C. is convenient and effective.Preferably, the temperature employed will bracket room temperature,i.e., from about 10° C. to about 30° C. Where water alone is used as thewash solvent, it will be employed at an elevated temperature, i.e.,above room temperature, preferably in a range of from about 25° C. toabout 40° C., most preferably, about 37° C.

Normally, it will be desirable to employ more than one wash step,typically two or three. After each such step, the microparticles will beseparated from the wash solution by well-known separation means, e.g.,filtration, decantation, centrifugation, and the like. Filtration ispreferred.

After each separation step, the microparticles can, if desired, be fullyor partially dried employing conventional drying means at temperaturessubstantially similar to those of the previous wash solution. The use ofdry compressed air at temperatures ranging from about 10° C. to about30° C. has been found especially useful and convenient and is preferred.

The microparticle product is usually made up of particles of a sphericalshape, although sometimes the microparticles may be irregularly shaped.The microparticles can vary in size, ranging from submicron tomillimeter diameters. Preferably, microparticles of 1-500 microns, morepreferably, 25-180 microns, are prepared, whereby administration of themicroparticles to a patient can be carried out with a standard gaugeneedle.

Preferably, the drug-loaded microparticles are dispensed to patients ina single administration, releasing the drug in a constant or pulsedmanner into the patient and eliminating the need for repetitiveinjections.

The active agent bearing microparticles are obtained and stored as a drymaterial. Prior to administration to a patient, the dry microparticlescan be suspended in an acceptable pharmaceutical liquid vehicle, suchas, a 2.5 wt. % solution of carboxymethyl cellulose, whereupon thesuspension is injected into the body.

The microparticles can be mixed by size or by type so as to provide forthe delivery of active agent to the patient in a multiphasic mannerand/or in a manner that provides different active agents to the patientat different times, or a mixture of active agents at the same time. Forexample, secondary antibiotics, vaccines, or any desired active agent,either in microparticle form or in conventional, unencapsulated form canbe blended with a primary active agent and provided to the patient.

Those skilled in the art will understand that any of the numerous activeagents that can be incorporated into microparticles can be prepared bythe process of the present invention. Preferred active agents for usewith the process of the present invention are those that contain atleast one basic moiety, such as a tertiary amine group. Particularly,preferred active agents for treatment by the process of the presentinvention are risperidone and 9-hydroxyrisperidone and thepharmaceutically acceptable salts thereof. For those materials that haveno groups detrimental to the integrity of the matrix polymer, theadditional washing step(s) of the present invention may prove beneficialin ways, such as, controlling the release characteristics of activeagent in vivo or reducing an undesirable or possibly harmful solvent.

The following examples further describe the materials and methods usedin carrying out the invention. The examples are not intended to limitthe invention in any manner.

EXAMPLE 1

In a typical 125 gram batch, 75 g of 75:25 Medisorb® lactide:glycolidecopolymer and 50 g of risperidone are dissolved in 275 g of benzylalcohol and 900.25 g of ethyl acetate as the organic phase. The aqueousphase comprises 90.0 g of polyvinyl alcohol, 8910 g of water, 646.4 g ofethyl acetate, and 298.3 g of benzyl alcohol. The organic and aqueousphases are pumped through a static mixer to form an emulsion. Theresulting emulsion is passed into a quench liquid comprising 17 kg ofwater, 4487.8 g of ethyl acetate, 371.0 g of sodium carbonate, and 294.0g of sodium bicarbonate. After 20 hours at approximately 10° C., theresulting microspheres are then filtered and washed with a first wash of11.25 kg of ethanol and 33.75 kg of water for 2 hours at 10° C. Themicrospheres are then filtered and washed with a solution of 11.25 kg ofethanol and 33.75 kg of water for 6 hours at 25° C. A third wash of 756g of citric acid, 482 g of sodium phosphate, and 45.0 kg of water isthen applied at 25° C. for one hour to the filtered product. The productis then rinsed with water, filtered, and dried. Three batches producedaccording to this procedure provide risperidone contents of 37.4%,37.0%, and 36.6% by weight. Benzyl alcohol levels were 1.36%, 1.26%, and1.38% by weight. Ethyl acetate levels were 0.09%, 0.08%, and 0.09% byweight.

EXAMPLE 2 Effect of the Wash Process on Microparticle Characteristics

A sample of risperidone-loaded microspheres was subjected to a series ofwash experiments to determine the impact on finished productcharacteristics and identify favorable wash conditions. The samplecomprised risperidone encapsulated in a 75:25 Medisorb®lactide:glycolide copolymer. The drug content was 36.8% by weight, andthe benzyl alcohol level was about 5.2% by weight prior to the washingexperiments. The microspheres were transferred into the wash media,samples were withdrawn at selected time periods and vacuum dried.

FIG. 1 shows the reduction in benzyl alcohol levels in the finishedproduct as a function of ethanol concentrations (5%; 15%; 20%; and 25%)in the ethanol:water wash. Higher ethanol levels afforded lower residualbenzyl alcohol in the finished product.

FIG. 2 shows that in the range of 0.1 to 1.0 liters of solution per gramof microspheres, the concentration of microspheres in the wash step doesnot influence the level of residual benzyl alcohol (BA) in the finishedproduct.

FIG. 3 shows the impact of temperature of the wash step on the level ofresidual benzyl alcohol in the finished product.

Table 1 shows an increase in glass-transition temperature (T_(g)) of thefinished microspheres as the wash time increases, and as theconcentration of ethanol increases and the corresponding concentrationof benzyl alcohol decreases.

                  TABLE 1    ______________________________________    Effect of Ethanol Wash Time and    Concentration on Glass Transition Temperature, T.sub.g    Wash Time             5%        15%       20%     25%    (Hours)  Ethanol   Ethanol   Ethanol Ethanol    ______________________________________    0.75     24.2° C.                       26.5° C.                                 30.1° C.                                         30.8° C.    3        26.5° C.                       26.5° C.                                 32.5° C.                                         35.1° C.    24       30.9° C.                       28.7° C.                                 37.3° C.                                         40.1° C.    ______________________________________

Risperidone-loaded microspheres with various levels of benzyl alcoholwere placed in stability studies at room temperature. FIG. 4demonstrates that the degradation process as measured by the rate ofhydrolysis of the biodegradable, biocompatible polymer is stronglyinfluenced by the level of residual solvent in the finished product. Themolecular weight decay constant was plotted versus residual benzylalcohol level for ten different microsphere samples.

While various embodiments of the present invention have been describedabove, it should be understood that they have been presented by way ofexample only, and not limitation. Thus the breadth and scope of thepresent invention should not be limited by any of the above describedexemplary embodiments, but should be defined only in accordance with thefollowing claims and their equivalents.

What is claimed is:
 1. A method of preparing biodegradable,biocompatible microparticles, comprising:(A) preparing a first phase,said first phase comprising an active agent, a biodegradable,biocompatible polymer, and a solvent; (B) preparing a second phase,wherein said first phase is substantially immiscible in said secondphase; (C) combining said first phase and said second phase under theinfluence of mixing means to form an emulsion in which said first phaseis discontinuous and said second phase is continuous; (D) immersing saidfirst phase and said second phase in a quench liquid that comprises aquench medium and a quantity of said solvent, wherein the quantity ofsaid solvent is selected to control a rate of extraction of said solventfrom said discontinuous first phase; and (E) isolating saiddiscontinuous first phase in the form of microparticles.
 2. The methodof claim 1, wherein said mixing means comprises a static mixer.
 3. Themethod of claim 1, wherein said solvent is a solvent blend of at leasttwo mutually miscible organic solvents.
 4. The method of claim 3,wherein one of said at least two organic solvents has a rate ofextraction from said discontinuous first phase that is more rapid than arate of extraction from said discontinuous first phase of another ofsaid at least two organic solvents.
 5. The method of claim 4, whereinsaid quantity of said solvent in said quench liquid comprises a quantityof said one of said at least two organic solvents having the more rapidrate of extraction and is free from said another of said at least twoorganic solvents.
 6. The method of claim 1, wherein said biodegradable,biocompatible polymer is selected from the group consisting ofpoly(glycolic acid), poly(d,l-lactic acid), poly(l-lactic acid), andcopolymers of the foregoing.
 7. A method of preparing biodegradable,biocompatible microparticles, comprising:(A) preparing a first phase,said first phase comprising an active agent, a biodegradable,biocompatible polymer, and a solvent blend comprising a first solventand a second solvent; (B) preparing a second phase, wherein said firstphase is substantially immiscible in said second phase; (C) combiningsaid first phase and said second phase under the influence of mixingmeans to form an emulsion in which said first phase is discontinuous andsaid second phase is continuous; (D) immersing said first phase and saidsecond phase in a quench liquid that comprises a quench medium and aquantity of said first solvent, wherein said first solvent has a rate ofextraction from said discontinuous first phase that is more rapid than arate of extraction from said discontinuous first phase of said secondsolvent, said quench liquid being free from said second solvent; and (E)isolating said discontinuous first phase in the form of microparticles.8. The method of claim 7, wherein said first solvent is ethyl acetateand said second solvent is benzyl alcohol.
 9. The method of claim 8,wherein said active agent is selected from the group consisting ofrisperidone, 9-hydroxyrisperidone, and pharmaceutically acceptable saltsthereof.
 10. The method of claim 7, wherein said quench liquid has aconcentration of said first solvent of from about 20% to about 70% of asaturation point of said first solvent in said quench medium.
 11. Themethod of claim 8, wherein said quench liquid has a concentration ofethyl acetate of from about 20% to about 70% of a saturation point ofethyl acetate in said quench medium.
 12. The method of claim 11, whereinsaid quench medium is water.
 13. The method of claim 7, wherein saidmixing means comprises a static mixer.
 14. The method of claim 7,wherein said biodegradable, biocompatible polymer is selected from thegroup consisting of poly(glycolic acid), poly(d,l-lactic acid),poly(l-lactic acid), and copolymers of the foregoing.
 15. Amicroencapsulated active agent prepared by a method for preparingbiodegradable, biocompatible microparticles, said method comprising:(A)preparing a first phase, said first phase comprising an active agent, abiodegradable, biocompatible polymer, and a solvent; (B) preparing asecond phase, wherein said first phase is substantially immiscible insaid second phase; (C) combining said first phase and said second phaseunder the influence of mixing means to form an emulsion in which saidfirst phase is discontinuous and said second phase is continuous; (D)immersing said first phase and said second phase in a quench liquid thatcomprises a quench medium and a quantity of said solvent, wherein thequantity of said solvent is selected to control a rate of extraction ofsaid solvent from said discontinuous first phase; and (E) isolating saiddiscontinuous first phase in the form of microparticles.
 16. Amicroencapsulated active agent prepared by a method for preparingbiodegradable, biocompatible microparticles, said method comprising:(A)preparing a first phase, said first phase comprising an active agent, abiodegradable, biocompatible polymer, and a solvent blend comprising afirst solvent and a second solvent; (B) preparing a second phase,wherein said first phase is substantially immiscible in said secondphase; (C) combining said first phase and said second phase under theinfluence of mixing means to form an emulsion in which said first phaseis discontinuous and said second phase is continuous; (D) immersing saidfirst phase and said second phase in a quench liquid that comprises aquench medium and a quantity of said first solvent, wherein said firstsolvent has a rate of extraction from said discontinuous first phasethat is more rapid than a rate of extraction from said discontinuousfirst phase of said second solvent, said quench liquid being free fromsaid second solvent; and (E) isolating said discontinuous first phase inthe form of microparticles.
 17. The method of claim 1, furthercomprising:(F) adjusting a temperature of said quench medium to controlsolubility of said solvent in said quench medium.
 18. The method ofclaim 7, further comprising:(F) adjusting a temperature of said quenchmedium to control solubility of said first solvent in said quenchmedium.
 19. The method of claim 8, further comprising:(F) adjusting atemperature of said quench medium to control solubility of said ethylacetate in said quench medium.
 20. The method of claim 19, wherein thetemperature of said quench medium is in the range of 0-10° C.